Method of reducing tubular products

Abstract

A method of reducing tubular metal products includes the steps of selecting a tube to be reduced having the specified initial wall thickness necessary to produce the desired finished wall thickness, and reducing the tube by passing it through a succession of roll stands which reduce the end portions of the tube without applying tension between roll stands and which reduce the portion of the tube intermediate the end portions with application of tension. The method produces reduced tubular products with substantially uniform wall thickness throughout eliminating the necessity of cropping end portions which have out-of-specification wall thickness.

What is claimed is: 
     
       1. A method of reducing tubular metal products comprising the steps of: (a) selecting a tubular member to be reduced having an initial wall thickness necessary to produce the desired finished wall thickness;   (b) processing said member through a reducing mill having successive rotating roll stands of decreasing roll groove diameters, the rotation speed differential between successive roll stands being variable;   (c) varying the roll rotation speed differential between successive roll stands as processing progresses to apply substantially no longitudinal tension to the tubular member as the front end portion enters and as the rear end portion leaves the roll stands, and to apply sufficient tension as the portion of the tube member intermediate the end portions is processed to restrict wall thickness increase in the intermediate portion to the same amount produced in the end portions.   
     
     
       2. The method of claim 1 wherein the tubular member to be reduced is selected having an initial wall thickness of t i  where ##EQU8## t f  =finished wall thickness desired (ends) ##EQU9## D i  =initial or entering tube or pipe diameter D f  =finished tube or pipe diameter x=outside diameter reduction (%) ##EQU10## and y=wall thickness increase % (ends) =0.017x 2 .   
     
     
       3. The method of claim 1 wherein the tubular product is reduced to a uniform wall thickness having zero crop end loss. 
     
     
       4. The method of claim 1 wherein the tubular metal product is steel tube. 
     
     
       5. A method of rolling speed control of a stretch reducing mill for hot reducing of the diameter of tubular members of ferrous or non-ferrous material wherein the roll rotation speed differential between successive roll stands is varied as rolling progresses to roll the tubular member substantially without longitudinal tension as the front end portion enters and as the rear end portion leaves the roll stands, and with sufficient tension as the portion of the tube member intermediate the end portions is rolled to restrict wall thickness increase in the intermediate portion to the same amount produced in the end portions.